1. Field of the Invention
The present invention relates to a rolled paper conveying apparatus, such as an image forming apparatus, a printer, a facsimile device, a cash register, or a ticket vending machine.
2. Description of the Related Art
Various machines, such as duplicating machines, printers, facsimile machines, registers, and ticket vending machines, use rolls of paper for generating a printed output. Rolled paper includes a plane body, such as light-sensitive paper, heat-sensitive paper, standard paper, or a film, which is wound around a core. Various methods are used to detect the end of rolled paper being used.
Rolled paper is generally defined as paper that is wound around a core. Furthermore, it is classified based upon whether end of the rolled paper is adhered to the core or is not adhered to the core. Generally, the end of the rolled paper is adhered to a core to avoid vibration of the end of the paper once the paper is completely unwound from the core. Additionally, the end of the paper is adhered to the core in order to easily wind the paper around the core during manufacturing.
Various methods are used to detect when an end of the paper of a rolled paper is reached. For example, the end of the rolled paper can be marked. Additionally, a method can be used that detects when the outer diameter of the rolled paper becomes small. (See, e.g., Japanese Patent Laid-Open No. Hei 1-38119.) Another method detects a conveyance speed of paper according to an outer diameter of the rolled paper becoming small with an encoder. (See, e.g., Japanese Patent Laid-Open No. Hei 5-16499.) Another method detects a tension between the core and the conveyance drives, where the tension is produced because of the conveyance drive pulling on the core. (See, e.g., Japanese Patent Laid-Open No. 2000-109256.) Furthermore, there is a method to add a detection device. (See, e.g., Japanese Patent Laid-Open No. 2000-136058.)
However, the above methods have various disadvantages. For example, a method of detecting a tension between a core and the conveyance drives may misinterpret tension that occurs when the machine starts or when rotational speed changes, since a temporarily high state tension can occur at these times. In this case, the problem also exists that the driving gear that is driven by a drive device can be broken by being overly pulled. In order to account for such a consideration, the drive device tends to become complicated, which increases the cost of the device.
Various methods require the use of a specific type of rolled paper, thereby limiting the choices of paper that can be used in a particular machine. Therefore, in addition to a specific kind of paper and a specific size, the user must also use a rolled paper having a specific type of marking that that allows the machine to detect the end of the rolled paper. For example, FIGS. 11(A)–(E) depict many different kinds of rolled paper having various markings. Another problem with such methods, the user may not be able to determine what kind of markings are used on a rolled paper until the paper is unrolled. Because, generally, until the paper is unrolled, the user cannot confirm what kind of markings are used. As a result, the machine cannot detect the markings precisely if the wrong kind of marking is used with a given detector.